Method of producing cellulosic material



Patented May 13, 1930 UNITED STATES PATENT OFFICE IBELA DORNER, OF BUDAPEST, HUNGARY, ASSIGNOR, BY MESNE ASSIGNMENTS, TO

1 CORNSTALK PRODUCTS COMPANY METHOD OF PBODUCII VG- CELLULOSIC MATERIAL No Drawing.-

This invention relates to the production of cellulose products from straw and other grasses and from cornstalks. Y

In the past, straw, cornstalks and grass, such as esparto grass, have been proposed as sources of cellulose and particularly of cellulose pulp for the production of paper. It has, however, not been possible to produce economically satisfactory paper pulp from these materials which have only been useful for certain coarse products such as strawnecessary to provide sufiicient liquor to cover the straw and cornstalks, but owing to their light weight, this amount of liquor is, of

course, greatly in excess of that actually re-.

quired to cook the weight of material present if it were in a form in which its specific gravity were not so low.

Straw and cornstalks possess a relatively smaller percentage of cellulose than does wood and much of the noncellulosie material consists in pentosans and similar carbohydrates or related materials which tend in the ordinary cooking processes to produce a waste liquor which is gummy and from which the chemicals cannot be recovered when, for example, caustic soda is used as the cooking agent. The products also contain a relatively considerable amount of silica, the percentage being notably in excess of that present in many pulp Woods. This results in a further serious loss of chemicals when the soda process is used, since the caustic soda units with the silica which is usually present in a hydrated form, producing alkali silicates which cannot be calcined and causticized to Application filed January 17, 1927. Serial No. 161,713.

straw lies in the fact that these products contain a cell structure which is relatively hard in certain pa'rtsof the material, especially in the oints and the external layers of the stalks. The material contains in addition to pentosans which are soluble in caustic soda-other colloidal organic substances which are not removed. The joints are not even sufiiciently disintegrated to permit removal ofpentosans as ordinary cooking at most softens them. As a result, a cooking process which is not carried out'to the extent of seriously disintegrating the cellulose itself will not remove all of the non-cellulosic materials and particularly will not attack satisfactorily the joints, so that the resulting pulp is of'poor color and difficult to bleach and contains hard dark nodules where the joints were only insufficiently disintegrated. High grade paper, thereforeycannot be; produced economically by the ordinary processes;

My present 'nvention permits the production of satisfactory grades of paper pulp-of. suitable light color from cornstalks, straw and the like, and at the same time minimizes or obviates losses of cooking liquor which have hitherto been unavoidable.

It is a' further object of the present invention to re.-

According to my invention, the treatmentof cornstalks, straw and thelike, is efiected in three definite stages. First, the stalks are shredded fine and are then leached with wa ter. either cold or hot. I have found that it is desirable, although by no means essential to the invention, that the shredded material be caused to flow very slowly in countercurrent to a slowly moving stream of water. Thus, for example, the shredded material can be gradually moved forward in a large tank in contact with water which slowly passes in a countercurrent. I have found,

for example, that a tank sufiiciently large to permit leaching for four or five days and provided with means for very slowly and con tinuously moving the shredded material forward in counter current to a slow flow of water, is very .satisfactory. Any other suitable leaching device, however, can be used and the particular apparatus forms no part of the present invention. This leaching re-- moves substantially all of the water soluble components of the material which are to a Very large extent saccharides, other sugars and salts. The material leached out may amount to some 8 or 10% or even more of the weight of the cornstalks or straw, depending, of course, on the material. The leach liquor may be evaporated to a'syrup which is a valuable addition to stock food. It is also possible to ferment the leachliquor to produce alcohol where this may prove to be advantageous. q

The leached cornstalks or straw still contain substantially all of their silica and also the large majority of the pentosans and other carbohydrates which were originally present and which, in many cases, amount to 40 or more percent of the weight of the material. The air cell structure between the fibers of the material is also still largely intact since, for leaching purposes, it is not necessary to completely disintegrate the air cells, as the water penetrates through the air cells and removes crystalloids by osmosis. The leached straw is then placed in a beater or any suit-' able device and is disintegrated to break I Thereafter, it is treated with an amount of alkali not materially in excess of that necessary to react with all of the silica. The .treatment with caustic soda may be subsequent to disintegra' tion in the beater or may take place in the beater itself. The temperature used may be substantially that of steam at ordinary. at-

mospheric pressures or it may be higher where a suitable closed beater or autoclave is used. The hotter the liquor, of course, the shorter the cooking time. I find, however, that for most purposes it is desirable to cook under substantially atmospheric pressure, as the use of expensive pressure-resisting beat ers or cookers is thereby obviated. In any event, the temperature should not be high enough to caramelize the pentosans, as otherwise their removal may be rendered difficult in further stages and a dark colored pulp may be prodqced and what is even more important the pentosans are rendered. unfit for feeding purposes. After cooking with the restricted amount of caustic soda solution, the waste liquor is drawn off and ifdesired the pasty mass may be washed with hot water. The liquorv contains sodium silicates and a small amount of pentosans. These latter may be precipitated by the cautious acidification, for example, withhydrochloric acid orany other suitable acid. The pentosans precipitate out, while the silicic acid remains substantially in solution. After removal by filtration, the )entosans may be used as such or if desired t ey may be added to the leach liquor from the first stage.

The partially cooked thoroughly disintegrated cornstalks or straw are then placed in an ordinary digester and are'cooked with caustic soda solution inlthe ordinary manner, care being taken, however, to keep the pressure of the digester and correspondingly the temperature 0 the cook below the point at which caramelization of pentosans take place. This temperature varies somewhat with the nature of-the' material used and, v

of course, to a certain extent on the strength art, I find that it is usually desirable to use pressures on the order of one or twoatmospheres, although it should be understood that the invention is in no sense limited to these lowcooking pressures, and in some cases higher pressures may be satlsfactorily used, and, of course, will resultin a quicker cooking. The nature of the materials varies considerably and no one set of conditions will operate perfectly with all of the grasses, with which the present invention is usable.

After cooking is complete, the waste liquor is drawn off, the pulp washed in the usual manner and bleached. The waste liquor, which contains large amounts of pentosans and other organic substances in loose chemical combination with the alkali, together with certain amounts of sodium carbonate and other products, is preferably treated with carbon dioxide which results in the precipitation of the pentosans and other organic substances, forming, of course, additional amounts of sodium carbonate. The pentosans may be separated by filtration, washed and used as such or purified or they may be added to the leach liquor of the first stage for use as stock foods or for any other purposes. 'lhe sodium carbonate filtrate, of course, can then be evaporated to dryness, as is the usual practice in the sodapulp art, followed by leaching and caustieizing or in many cases I have found that it is not necessary to evaporate the solution, but, on the contrary, it may be directly causticized. Of

course, the feasibility of direct causticizain a satisfactory manner producing an excellent grade of pulp and at the same time recovering in a commercial, usable form the 1na]ority of the non-cellulosic components.

A large and important new field of raw ma terials, is therefore opened up for the production of paper pulp and at the same time large quantities of straw and cornstalks which have hitherto been burned as fuel or thrown away are made available for profitable exploitartion.

. While it is usually desirable to utilize all of the steps of the present invention and to produce high grade pulp from straw, cornstalks and the like, it should be understood that the invention is not limited to the use of all of the steps of the process. On the contrary, it is sometimes desirable to stop at an intermediate point. Thus, for example, when J certain grades of strawboard are to be made,

as it tends to dull tools used in cutting it.

This is particularly important in the case of wall boards of considerable thickness. It should also be understood that while it is desirable to separate out the silica in a separate step, it may sometimes prove more advantageous, particularly where the silica content is not high, to cook the leached and disintegrated material with suflicient caustic soda to produce in one step pulp of satisfactory character.- This will usually result in-a considerably higher loss of caustic soda, but under some conditions the saving in the omission of one of the steps may more than counterbalance the additional loss of chemicals and such a process in which one of the intermediate steps or stages is omitted is included within the scope of the present invention.

The invention has been described in connection with'the use --of caustic soda, but, of

course, other caustic alkalies maybe used Wherever they are available at satisfactory prices.

. In the claims, the expression strawlike body or material is intended to include such strawlike stalks as cornstalks, flax, .esparto grass, etc.

y This application is in part a continuation of in prior application Serial No. 158,421, filed lDecember 31, 1926.

Having thus described my invention, What' I desire to secure by Letters Patent of the United States and claim is:

1. A method of producing cellulosic material from straw-like bodies which comprises leaching out the water soluble constituents by conveying the straw-like material slowly counter to a slowly moving stream of water, and subjecting the leached material to cooking with a suitable chemical solution.

2. 'A method of producing cellulosic material from straw-like bodies which comprises leaching out the water soluble components of the strawlike bodies, subjecting the leached material to mechanical disintegration of its cell structure, bringing the disintegrated material into contact with heated caustic alkali solution in amount not materially in excess of that necessary to remove all of the silica present, separating the liquor from the disintegrated material, and cooking the material with a further quantity of caustic alkali solution.

3; A method according to claim 2, in which the cooking steps are carried out at a temperature below that at which carbohydrate material present is substantially caramelized.

4. A method ofetreating waste liquors containing alkali silicates and the reaction products of difiicultly soluble carbohydrate material and caustic alkali which comprises acidifying the liquor to a point at which substantially all of the carbohydrates material is freed from chemical combination with the alkali and precipitated and at which the silica remains in solution.

5. In the method of producing cellulosic material from straw-like bodies, the improvements which comprise mechanically disintegrating the cell structure of a strawlike body, subjecting the product to cooking with an amount of alkali not materially in excess of that necessary to react with all ofthe silica present at a temperature below that at which insoluble carbohydrate material is notably caramelized, removing liquor from the prodnot, and treating the liquor with an amount of acid to set free substantially allof the carbohydrate material and at which the silica remains in solution.

6. A method of producing cellulosic material from straw-like bodies which comprises leaching out the water soluble constituents of the straw-like bodies, subjecting the leached material to cooking with an amount of caustic soda which is not materially in excess of that necessary to react with all of the silica present at a temperature below that at which substantial amounts of insoluble carbohydrate materials present are caramelized, removing the liquor from the product, separating out the carbohydrate material therefrom, cooking the treated material with a r present, removing the liquor from the remaining cellulosie material, precipitating the carbohydrates by treatment with an acidic substance which forms with caustic alkali a causticizable compound, and regenerating caustic alkali from said liquor.

8. A method according to claim 7 111 which the acidic substance used 18 carbon d1- 9. In a method of producing cellulosic material from straw-like bodies, the improvements which comprise conveying the straw like material slowly counter-current to a stream of water so as to leach out the water soluble constituents from said material and recovering the water soluble constituents from the leaching water.

10. The process of liberating cellulose from straw-like bodies containing silica, which comprises removing said silica by means of a solution of an alkali of a strength insufficient to materially affect the cellulose and non-cellulose constituents of the straw-like bodies, and thereupon treating the desilicalized material with a solution of caustic soda to dissolve organic,non-cellulosic materials, whereby the fiber is liberated.

11. The process of fiber liberation from shredded corn stalks which comprises removing silica therefrom by heating them with-a very dilute solution of a caustic alkali, said solution being too weak in alkali to afiect materially the organic non-cellulosic constituents of said stalks and thereupon subjecting the desilicalized material thus obtained to treatment with alkaline solutions of sufiicient strength to remove from the material tljpe non-cellulosic organic constituents there- 0 Signed at New York, New York, this 12th day of January, 1927.

BELA DORNER. 

